Method and Arrangements for an Event Triggered DRX Cycle

ABSTRACT

The invention relates to methods and arrangements for an event triggered DRX cycle adjustment. A user equipment located in a serving cell of a mobile communications network monitors downlink communication at predetermined time intervals when operating in discontinuous reception mode. The user equipment also performs communication parameter measurements regarding at least one of the serving cell and one or more neighbor cells. After the occurrence of a first event, the user equipment sends at least one of measurement data and a first event report to the network. The sending is triggered by the occurrence of the first event. The monitoring is caused to be performed at shortened time intervals after the occurrence of a second event, wherein the second event is defined to indicate a higher probability of receiving a handover command than the first event.

TECHNICAL FIELD

The present invention relates to methods and arrangements in atelecommunication system, in particular to methods and arrangements foran event triggered DRX cycle adjustment.

BACKGROUND

Among others the following definitions and abbreviations will be used inthe description below.

ASIC Application Specific Integrated Circuit

CPICH Ec/No The received energy per chip divided by the power density inthe band

CPICH RSCP Common Pilot Channel Received Signal Code Power DRXDiscontinuous Reception DTX Discontinuous Transmission eNB E-UTRAN NodeBE-UTRA Evolved UTRA E-UTRAN Evolved UTRAN FDD Frequency Division DuplexLTE Long Term Evolution MAC Medium Access Control RRC Radio ResourceControl RRM Radio Resource Management RSRP Reference Signal ReceivedPower RSRQ Reference Signal Received Quality

SINR Signal to Interference plus Noise Ratio

UE User Equipment UTRA Universal Terrestrial Radio Access UTRANUniversal Terrestrial Radio Access Network TTI Transmission TimeInterval

WCDMA Wide band Code Division Multiple Access

Universal Terrestrial Radio Access Network (UTRAN) is a conceptual termthat identifies that part of the network which consists of Radio NetworkControllers (RNCs) and Node Bs. This communications network is commonlyreferred to as 3G. Evolved UTRAN (E-UTRAN) is an evolution of the 3Gradio access network towards a high-data rate, low-latency andpacket-optimised radio access network.

The document 3GPP TS 36.300, V 0.3.1 (2006-11) provides an overview andoverall description of the E-UTRAN radio interface protocolarchitecture.

The E-UTRAN is fundamentally a packet oriented system. This means thatusers transmit and receive data in non-continuous fashion. One importantimplication is that at a given time not all the users are active (i.e.not all the active users communicate simultaneously). This inherentcharacteristic of packet transmission is intended to be fully exploitedin E-UTRAN system.

One important aspect of packet transmission is discontinuoustransmission (DTX) and discontinuous reception (DRX). The E-UTRAN isprimarily a packet-oriented system without any circuit switchedtransmission. This means that E-UTRAN can easily be optimized for packettransmission. One important feature introduced in E-UTRAN is thepossibility of UE entering into DRX mode. In E-UTRAN there are three UEstates with their context stored in the core network:

-   -   LTE_DETACHED    -   LTE_IDLE    -   LTE_ACTIVE

However, only the last two states also have RRC context. Therefore, fromradio resource allocation and usage perspective the last two states arethe most interesting ones and are therefore further described below:

In the LTE_IDLE state the UE listens to the network (e.g. by means ofpaging information) only at DRX instant and performs downlinkmeasurements according to the assigned DRX cycle length and autonomouscell reselection. In order to receive data the UE needs to enter intoLTE_ACTIVE state, which is an essential feature in all cellular systemsto allow UE battery saving.

In the LTE_ACTIVE state the UE is able to receive data and transmit dataat any time. This implies that the network maintains the full RRCcontext on cell level in order to be able to schedule the user wheneverrequired. (For this reason this state is also called RRC connected stateon RRC level). The LTE_ACTIVE state has a sub-state called the DTX/DRXmode for the purpose of saving UE battery is consumption in case of lowactivity. After a certain period of inactivity the UE enters into thissub-state and starts monitoring the downlink transmitted informationonly at a regular interval according to the network assigned DRX cycle.The DRX cycle in this case can vary typically between 5 ms up to 1-5seconds. However, in case of much longer inactivity of packets the UEshould preferably enter into idle mode.

The advantages of the type of DRX/DTX mode described above are that, onthe one hand, it allows efficient UE battery savings while, on the otherhand, the network can quickly schedule a UE without unnecessary delayscaused by the formalities of the call setup procedure. The concept ofthe DRX/DTX sub-state in RRC connected state is also used in UTRA incontinuous packet connectivity, which comprises purely packet orientedtransmission.

Downlink scheduling information is used to inform the UE how to processthe downlink data transmission. The scheduling information may includethe UE identity, resource assignment, duration of assignment, modulationscheme, etc. and may be sent on a shared control channel, whichcomprises of mainly layer 1 (physical layer) and layer 2 (MAC layer)contents. Generally, this information is sent in every sub-frame (0.5ms) or at least every TTI (e.g. 1 ms). Therefore, a UE in LTE_ACTIVEmode may have to monitor this information in every sub-frame or TTIdepending upon the periodicity of the transmission of schedulinginformation.

The handover in LTE_ACTIVE state is network-controlled. This means thatthe UE reports measurements to the network in response to an event. Anevent occurs when one or more parameters take on a certain value orcertain values. En event can for instance be configured to occur whenone parameter reaches a certain value individually, or when oneparameter reaches one value and another parameter reaches another value,i.e. as a combination of different parameter values. The event and/ormeasurement reporting either triggers idle gaps for more measurement(e.g. on other carrier frequency or other technologies) or leads tohandover. During an idle gap the UE tunes its receiver to another E-UTRAcarrier frequency or to a carrier frequency of another access technology(e.g. UTRA or GERAN) for performing the measurements. While performingsuch measurements the UE does not receive or transmit any data orsignaling information on the serving E-UTRA carrier frequency. In thecase of handover the UE receives a handover command from the network. InDRX mode in LTE_ACTIVE state the UE can receive any network information(e.g. scheduling of handover command) only at the DRX instant, i.e. whenthe UE becomes active. In case of long DRX cycle (e.g. 2 or 3 seconds)the handover command reception can be delayed. But to ensure good systemperformance (low handover latency) both the UE measurement reporting andhandover command reception should not be delayed. At the same time thecharacteristics of DRX mode should be retained to ensure efficient UEbattery consumption.

In E-UTRAN the UE reports in the LTE_ACTIVE state the configured eventsand the corresponding downlink measurements when the network configuredevent criteria or conditions are fulfilled. As indicated above, the UEcan also, in an LTE_ACTIVE state, operate in DRX mode in which the UEmonitors the downlink scheduling channel only at DRX instances. In orderto prevent handover delay, it has been agreed that at the occurrence ofan event the UE shall report both the measurement quantity and the eventas quickly as possible without waiting for the next active period.

Another important aspect is the delivery of the handover command inresponse to the event triggered measurement reporting. Since the UElistens periodically only at DRX instances, this can unnecessarily delaythe handover command reception especially in case of long DRX cycle. Butin order to ensure low handover latency the handover command, wheneverrequired, should be delivered to the UE as soon as possible. It hastherefore also been agreed that the UE shall interrupt its DRX activityafter each and every event triggered measurement report and startmonitoring the scheduling control channel either continuously oraccording to a pre-configured shorter DRX cycle. This will allow thenetwork to schedule the UE immediately for the purpose of sending ahandover command. One major drawback with this approach is that in casethe network does not send handover command the UE battery will beinefficiently utilized.

There are several reasons why the network may not send a handovercommand in response to an event-triggered measurement report:

-   -   The network may set lower threshold to get more frequent events        for monitoring network performance (e.g. operational and        maintenance issues).    -   Another reason is that event triggered report may not directly        lead to a handover; rather this may trigger gap-assisted        measurements (e.g. measurements on another frequency or on        another access technology).    -   A particular UE measurement report may also be utilized for RRM        functions other than handovers such as congestion control etc.    -   Depending upon the implementation not all measurements may        trigger handover or at least some measurements may not directly        trigger the handover. As an example in WCDMA the UE transmitted        power reporting (and corresponding event) is used in the network        to trigger the compressed mode. UTRAN can command that the UE        enters into compressed mode depending on UE capabilities, which        define whether the UE requires compressed mode in order to        monitor cells on other FDD frequencies and on other modes and        radio access technologies.    -   Depending upon a particular implementation the network may        perform handover according to combination of measurements, e.g.        based on UE transmitted power and downlink received SINR.

Thus, there are a number of cases in which the network does not send ahandover command in response to an event triggered measurement report,whereby the following control channel monitoring leads to excess batteryconsumption in the prior art solution.

SUMMARY

It is an object of the present invention to overcome or at leastalleviate some or all of the above-mentioned drawbacks of the prior art.Specifically, it is an object of the present invention to achieve atechnique that alleviates the conflict between low power consumption andfast handover command reception in a user equipment that operates tomonitor downlink communication at predetermined time intervals, e.g.given by a DRX cycle.

These and other objects, which will be apparent from the followingdescription, are achieved completely or partially by means of a methodin a user equipment, a method in a base station, a user equipment, and abase station according to the appended independent claims. Preferredembodiments are defined in the dependent claims.

The invention overcomes the problem of excess battery consumption in theUE due to unnecessary control channel monitoring by seeking todistinguish the case of handover command reception from the other cases.

This is achieved by the definition of new, additional event thatspecifically relates to this case.

From the UE battery consumption perspective it is beneficial to havethis specific event that indicates a high probability of handover. Onlyat the setting of this particular event the UE should perform monitoringat shortened time intervals, by e.g. disregarding the DRX operation andentering into non DRX mode where it starts continuous monitoring of thedownlink scheduling control channel.

The UE monitors the scheduling control channel at shortened timeintervals, e.g. either continuously or according to a pre-configuredshorter DRX cycle (i.e. non DRX mode), only when there is more certaintyof receiving the handover command. This means the UE shall not monitordownlink communication at shortened time intervals, e.g. by enteringinto non DRX mode, in response to normal measurement reporting. Thus,the occurrence of the original first event, which has been described inthe background section, does not cause monitoring to be performed atshortened time intervals. Instead the UE shall perform schedulingcontrol channel monitoring at shortened time intervals, e.g. by enteringnon DRX mode, only in response to an event specifically meant for thispurpose.

Hence the present invention defines a separate event that triggersmonitoring of downlink communication at shortened time intervals, e.g.by triggering the non DRX mode at the UE for the reception of handovercommands. In other words the normal measurement reporting is notdirectly linked to shortened time intervals, or e.g. the non DRXoperation. This is because all measurement reports may not directly leadto handover. This will allow better UE power saving.

The invention relates in one aspect to a method in a user equipment thatis located in a serving cell of a mobile communications network.According to the method downlink communication is monitored atpredetermined time intervals when the user equipment is operating indiscontinuous reception mode. Also, communication parameter measurementsregarding at least one of the serving cell and one or more neighbourcells are performed. After the occurrence of a first event, at least oneof measurement data and a first event report is sent from the userequipment to the network. The sending is triggered by the occurrence ofthe first event. Furthermore, the monitoring is caused to be performedat shortened time intervals after the occurrence of a second event. Thesecond event is defined to indicate a higher probability of receiving ahandover command than the first event.

In a second aspect, the invention relates to a method in a base stationin a cell of a mobile communications network. A user equipment in thecell monitors downlink communication at predetermined time intervalswhen operating in discontinuous reception mode, and performscommunication parameter measurements regarding at least one of theserving cell and one or more neighbour cells. According to the method, afirst event is configured in the user equipment. The occurrence of thefirst event triggers sending of at least one of measurement data and afirst event report from the user equipment to the base station. Also,the method comprises configuring a second event in the user equipment.The occurrence of the second event causes the monitoring to be performedat shortened time intervals. The second event is defined to indicate ahigher probability of sending a handover command to the user equipmentthan the first event.

According to a third aspect of the invention, a user equipment locatedin a serving cell of a mobile communications network is provided. Theuser equipment comprises means for monitoring downlink communication atpredetermined time intervals when operating in discontinuous receptionmode. Also, means for performing communication parameter measurementsregarding at least one of the serving cell and one or more neighbourcells are comprised.

Furthermore, it comprises means for sending at least one of measurementdata and a first event report from the user equipment to the networkafter the occurrence of a first event. The sending is triggered by theoccurrence of the first event. The user equipment also comprises meansfor causing the monitoring to be performed at shortened time intervalsafter the occurrence of a second event. The second event is defined toindicate a higher probability of receiving a handover command than thefirst event. The means utilised according to this third aspect, such asnecessary antenna and radio equipment, are all standard user equipmentcomponents well known to a person skilled in the art. Also, the meansfor triggering monitoring to be performed at shortened time intervalscould be implemented as for instance software that is run on one or moreprocessors in the user equipment. Alternatively it could possibly beimplemented by hardware, such as one or more ASICs.

In a fourth aspect, the invention relates to a base station in a cell ofa mobile communications network. A user equipment in the cell monitorsdownlink communication at predetermined time intervals when operating indiscontinuous reception mode, and performs communication parametermeasurements regarding at least one of the serving cell and one or moreneighbour cells. The base station comprises means for configuring afirst event in the user equipment, whereby the occurrence of the firstevent triggers sending of at least one of measurement data and a firstevent report from the user equipment to the base station. It alsocomprises means for configuring a second event in the user equipment,whereby the occurrence of the second event causes the monitoring to beperformed at shortened time intervals. The second event is defined toindicate a higher probability of sending a handover command to the userequipment than the first event. The means utilised according to thisfourth aspect, such as antenna and radio equipment, are all standardbase station components well known to a person skilled in the art.Software run on e.g. a processor in the radio base station could be usedfor logical operations, such as how to configure the first and thesecond events, respectively.

The present invention offers the advantage to allow a more efficient useof UE battery saving, by defining a new, second event that occurs whenthe probability of receiving a handover command in a user equipment ishigh.

It is another advantage of the present invention to provide moreflexibility to the network in terms of threshold setting, since a numberof different parameters and corresponding parameter values can be usedto trigger downlink communication monitoring at shortened timeintervals.

It is yet another advantage of the present invention to provide moreflexibility to the network in terms of using a particular UE measurementfor a purpose other than handover (e.g. O&M, triggering gap-assistedmeasurement, congestion control etc) but can still ensure good UE powersaving.

Another advantage of the invention is that it can be used for othertelecommunication network standards than E-UTRAN, such as WCDMA or GSMnetworks, in cases where those standards utilizes correspondingmeasurements and handover command schemes.

Further objectives, features, aspects and advantages of the presentinvention will appear from the following detailed disclosure, from theattached dependent claims as well as from the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplifying embodiments of the invention will now be described in moredetail with reference to the accompanying schematic drawings.

FIG. 1 schematically illustrates the general architecture in whichembodiments of the invention can be used.

FIG. 2 schematically illustrates a user equipment for which embodimentsof the invention can be used.

FIG. 3 schematically illustrates a radio base station for whichembodiments of the invention can be used.

FIG. 4 illustrates a block diagram of the general flow of a method in auser equipment according to an embodiment of the invention.

FIG. 5 illustrates a block diagram of the general flow of a method in abase station according to an embodiment of the invention.

FIG. 6 is a conceptual illustration of an embodiment of the invention.

FIG. 7 illustrates an event configuration at the UE to enter into anon-DRX mode for handover command reception according to an embodimentof the invention.

FIG. 8 illustrates an example of an event reporting and handover commandreception in DRX-mode according to an embodiment of the invention.

FIG. 9 illustrates a switching to a non-DRX-mode in order to receive ahandover command according to an embodiment of the invention.

DETAILED DESCRIPTION

FIG. 1 shows the general architecture in which embodiments of theinvention may be used. A mobile station 10, or user equipment (UE), islocated within the coverage of a mobile communications network. The UEcommunicates with base stations 20, or E-UTRAN NodeB:s (eNB:s) in thecase of LTE, which provides wireless network coverage for a particularcoverage area commonly referred to as a cell 30. The cell 30 in whichthe UE 10 resides at a given moment is referred to as the serving cell.Neighbour cells are located adjacent to the serving cell. The eNBs areinterconnected, and are also connected to the EPC (Evolved Packet Core),and more specifically to the MME (Mobility Management Entity) and to theServing Gateway (S-GW). Radio Resource Control (RRC) terminates in eNB,and measurement configuration is done via RRC, which resides in eNB.FIG. 2 schematically shows a UE 10 that comprises standard wirelessdevice components, such as an antenna arrangement, radio equipment, alogic unit that can be implemented for instance as a microprocessor, aCPU, or similar processing or computer means, as well as some kind ofdata storage unit or memory unit. The skilled person will realize that auser equipment comprises these and other components, and they willtherefore not be described further in this application. The UE 10 inFIG. 2 comprises means 111 for monitoring downlink communication atpredetermined time intervals, means 112 for performing communicationparameter measurements, and means 113 for sending measurement data fromthe UE 10 to the network, whereby the sending is triggered by theoccurrence of a first event. The UE 10 also comprises means 114 forcausing the monitoring to be performed at shortened time intervals afterthe occurrence of a second event, which is defined to indicate a higherprobability of receiving a handover command than the first event.

FIG. 3 schematically shows a network radio base station 20 that may beused in connection with the present invention. It comprises standardradio base station components, such as network interfaces, an antennaarrangement, radio equipment, a logic unit that can be implemented forinstance as a microprocessor, a CPU, or similar processing or computermeans, as well as some kind of data storage unit or memory unit. Theradio base station 20 in FIG. 3 comprises means 211 for configuring afirst event in a UE 10, whereby the occurrence of the first eventtriggers sending of measurement data from the UE to the base station. Italso comprises means 212 for configuring a second event in a UE 10,whereby the occurrence of the second event causes monitoring to beperformed at shortened time intervals. The second event is defined toindicate a higher probability of sending a handover command to the UE 10than the first event. Furthermore, the radio base station 20 comprisesmeans 213 for defining the first event and the second event in relationto parameter measurements. For instance, the means 213 may according toembodiments of the invention be used to configure that the second eventshall occur when e.g. measured downlink quality and/or user equipmenttransmitted power reaches certain levels. The configuration of an eventmay imply that the radio base station signals the user equipment a setof specific parameters, such as threshold levels, time to trigger, etc,corresponding to that event.

FIG. 4 shows steps of a method in a UE 10 that are carried out accordingto embodiments of the invention. First, in s100 the UE 10 monitorsdownlink communication at predetermined time intervals. In s110 the UE10 performs communication parameter measurements. Then, in s120, the UE10 sends measurement data and/or a first event report to the network.The sending is triggered by the occurrence of a first event. In s130 thetime intervals for performing monitoring are shortened as an effect ofthe occurrence of a second event. The second event is defined toindicate a higher probability of receiving a handover command than thefirst event.

According to embodiments of the invention, a method in a base station 20is illustrated in FIG. 5. The base station 20 is located in a servingcell of a mobile communications network, wherein a UE 10 in the cellmonitors downlink communication at predetermined intervals and performsparameter measurements. First, the base station 20 in s200 configures afirst event in the UE 10, whereby the occurrence of the first eventtriggers sending of measurement data and/or a report, or message, thatindicates the occurrence of the first event from the UE 10 to the basestation 20. In s210 the base station 20 configures a second event in theUE 10. The occurrence of the second event causes the monitoring to beperformed at shortened time intervals. Furthermore, the second event isdefined to indicate a higher probability of sending a handover commandto the UE 10 than the first event.

FIG. 6 is a conceptual illustration of an embodiment of the invention,exemplified by a case in which DRX cycles are used. A general prior artproblem is that a UE 10 shortens its monitoring time intervals aftereach first event occurrence, since a handover command might be sent fromthe network. However, since a number of other actions that do notrequire a time interval shortening might be carried out by the network,this is done unnecessarily in many cases. This leads to unnecessarilyhigh UE battery consumption.

Hence, the invention distinguishes the case of handover from the othercases by defining a specific second event, which indicates a higherprobability of receiving a handover command in the UE 10. The event initself can occur for a number of different parameter settings orconfigurations, of which some will be described below. Both the firstand the second event are defined in relation to parameter measurements.

According to embodiments of the invention, at first the network needs toconfigure an event (E₂) that is specific to non-DRX mode at the UE 10,see FIG. 7. A person skilled in the art will realize that theconfiguration may take place in a network base station in the case ofLTE. The event, E₂, is described in the next section. Non-DRX-modedenotes here is the state where a UE 10 either continuously (i.e. everysub-frame or TTI) monitors the downlink scheduling control channel oraccording to a shorter DRX cycle. The monitoring of downlinkcommunication is thus caused to be performed at shortened timeintervals. The event configuration, as well as the configuration of theshortened time intervals, may be done in the measurement control messageor any other signaling message using RRC signaling. The configuredparameters may include:

-   -   Downlink measurement quality threshold (X₂) above which the UE        enters into non DRX mode. For LTE, RSRQ can be used as the        measured parameter. For WCDMA, CPICH Ec/No may be a relevant        quality measurement.    -   Time to trigger. During this time period parameter measurements        may be verified in the UE 10 in order to make sure that the        conditions configured for the occurrence of an event are        fulfilled more than on one occasion. A network base station 20        may configure the conditions for continued measurement during        the time to trigger, whereby means 211-213 can be used.    -   DRX cycle length after the event E₂. This could be specified as        DRX cycle before E₂/M; where M is set by the network. As an        example if M is set such that DRX cycle length after E₂=0.5 ms,        then the UE 10 monitors continuously or moves into a fully        connected mode. Thus the parameter M can specify the length of        the time intervals at which the UE 10 shall monitor the        scheduling control channel after event E₂ occurs.    -   The minimum amount of time during which the UE 10, if not        scheduled, remains in non DRX state after the occurrence of        event E₂. This can be specified in terms of N number of        sub-frames, TTI, frames, DRX cycle lengths, or simply time        duration.

According to embodiments of the invention the UE 10 monitors thescheduling control channel either continuously or according to apre-configured shorter DRX cycle only when there is more certainty ofreceiving the handover command. The main benefit of this approach isthat in case handover command is not required in response to the normalmeasurement reporting event (E₁) the UE 10 will not waste its power bycontinuous monitoring of scheduling control channel.

This requires an additional event configuration in the UE 10. Oneexample is shown in FIG. 8, in which the parameter measured downlinksignal quality is used to define when events shall occur. The event (E₂)can be configured to occur at a different threshold level compared to athreshold level configured for the occurrence of the first event asshown in the figure. The second event can be configured to occur whenone or more measurement quantities deteriorate beyond a certain level.As an example the new event (E₂) can occur when UE transmitted power isabove a certain threshold and the downlink SINR is below anotherthreshold. In one embodiment according to the invention the second eventoccurs when the user equipment transmitted power rises above a set leveland when the measured downlink signal quality goes below another setlevel. Also, UE received power may be used as a suitable parameter fordefining when events shall occur. For LTE, RSRP is a UE received powermeasurement and RSRQ is a UE received quality measurement that may beused in combination or individually. For WCDMA, the parameters CPICHRSCP and CPICH Ec/No, respectively, may be suitable parameters. Asbefore, the threshold values used in E₂ can be different compared tothose used in E₁.

The new event (E₂) is defined to indicate a higher probability ofreceiving a handover command in a user equipment than the original firstevent, which has been described in the background section.

FIG. 8 depicts that the UE 10 starts continuous monitoring of thescheduling channel (or with shorter pre-configured DRX cycle) at theonset of an event E₂. As shown in the figure the threshold set for theevent E₂ is higher than for the event E₁. The example in FIG. 8 depictsan embodiment in which the measured downlink quality is used fordetermining whether the second event shall occur. The parameter RSRQ canbe used in the case of LTE. The second event, whose occurrence triggersmonitoring to be performed at shortened time intervals, occurs when thedifference in measured downlink quality between the serving cell and aneighbour cell reaches a set level. The occurrence of only the firstevent, E₁, does not cause any change in the monitoring time intervals.

According to another embodiment, the second event is configured to occureither when the measured downlink quality goes below a set level or whenthe user equipment transmitted power rises above another set level.Hence, as soon as either one of the parameters reaches a certain levelthe second event occurs. Also, as mentioned before, the parameters RSRQand RSRP may be suitable in the case of LTE. It is to be understood thatall parameters mentioned in this description may be used individually,as well as in combination, in order to define when the second eventshall occur. For instance, the second event may occur when the userequipment transmitted power rises above a predetermined level.

The skilled person will, based on the examples described above, realizethat other parameter configurations and combinations also may be used todecide when the second event shall occur.

A different time to trigger values can be used for the two events. Theevent E₁ as stated before is a normal measurement reporting event. Itcould be that event E₁ only triggers gap-assisted measurement on anothercarrier instead of handover. It may also lead to some other networkaction such as, e.g., congestion control. The main advantage ofutilizing the method based on the second event (E₂) is that UE can makemore efficient use of battery consumption since the probability ofhandover command reception will be higher.

It is still probable, though less likely that UE 10 will not receivehandover commands after the occurrence of event E₂. But in order tocater for this rare scenario the UE 10 may again revert to the normalDRX cycle in case it is not scheduled for certain duration (e.g. after Nsub-frames or frames) as configured by the network.

FIG. 9 shows an embodiment of the invention in which the UE maintainsthe on going DRX cycle after reporting event E₁, which is the normalmeasurement reporting. On the other hand the UE 10 enters into non DRXmode (i.e. either continuous monitoring of scheduling control channel oraccording to a shorter DRX cycle) after reporting event E₂. Firstly, theUE 10 receives the scheduling information, comprising of resourceblocks, sub-frames, frame number etc on which the UE 10 shall bescheduled to receive the handover command. The UE 10 eventually receivesthe handover command on the assigned resource blocks.

The above described embodiments of the invention are intended to beexamples only. Alterations, modification, and variations may be effectedto particular embodiments by those skilled in the art without departingfrom the scope of the invention, which is defined by the accompanyingclaims.

For instance, even though the above description uses the terms firstevent and second event, respectively, a person skilled in the art willrealize that terms like first and second configuration, or first andsecond setting could be used to the same effect.

1. A method in a user equipment located in a serving cell of a mobilecommunications network, said method comprising: monitoring downlinkcommunication at predetermined time intervals when operating indiscontinuous reception mode, performing communication parametermeasurements regarding at least one of the serving cell and one or moreneighbor cells, and after the occurrence of a first event, sending atleast one of measurement data and a first event report from said userequipment to said network, wherein said sending is triggered by theoccurrence of the first event, wherein said monitoring is caused to beperformed at shortened time intervals after the occurrence of a secondevent, wherein said second event is defined to indicate a higherprobability of receiving a handover command than said first event. 2.The method according to claim 1, wherein said first event and saidsecond event are defined in relation to said parameter measurements. 3.The method according to claim 1, wherein said second event occurs whenthe difference in measured downlink signal quality between the servingcell and a neighbor cell reaches a predetermined level.
 4. The methodaccording to claim 1, wherein said second event occurs when the measureddownlink signal quality deteriorate beyond a predetermined level or whenthe user equipment transmitted power exceeds a predetermined level. 5.The method according to claim 1, wherein said second event occurs whenthe user equipment transmitted power exceeds a predetermined level andthe measured downlink signal quality decreases below a predeterminedlevel.
 6. The method according to claim 1, wherein said monitoring atshortened time intervals is caused after a predetermined time periodfrom said occurrence of said second event.
 7. The method according toclaim 6, wherein said parameter measurements are continued to be carriedout during said predetermined time period from said occurrence of saidsecond event in order to verify that the conditions for said secondevent are fulfilled during the predetermined time period.
 8. The methodaccording to claim 1, wherein said second event is configured by thenetwork.
 9. The method according to claim 1, wherein the shortened timeintervals after said second event occurs are set by the network.
 10. Themethod according to claim 1, wherein the predetermined time intervalscorrespond to a predetermined DRX cycle.
 11. A method in a base stationin a serving cell of a mobile communications network, wherein a userequipment in the cell monitors downlink communication at predeterminedtime intervals when operating in discontinuous reception mode andperforms communication parameter measurements regarding at least one ofthe serving cell and one or more neighbor cells, said method comprising:configuring a first event in the user equipment, the occurrence of whichtriggers sending of at least one of measurement data and a first eventreport from the user equipment to the base station, and configuring asecond event in the user equipment, the occurrence of which causes saidmonitoring to be performed at shortened time intervals, whereby saidsecond event is defined to indicate a higher probability of sending ahandover command to the user equipment than said first event.
 12. Themethod according to claim 11, wherein said first event and said secondevent are defined in relation to said parameter measurements.
 13. Themethod according to claim 11, wherein said second event occurs when thedifference in measured downlink signal quality between the serving celland a neighbor cell reaches a set level.
 14. The method according toclaim 11, wherein said second event occurs when the measured downlinksignal quality deteriorate beyond a predetermined level or when the userequipment transmitted power exceeds a predetermined level.
 15. Themethod according to claim 11, wherein said second event occurs when theuser equipment transmitted power exceeds a predetermined level and themeasured downlink signal quality decreases below a predetermined level.16. The method according to claim 11, wherein said monitoring atshortened time intervals is triggered after a predetermined time periodfrom said occurrence of said second event.
 17. The method according toclaim 16, wherein parameter measurements are continued to be carried outduring said predetermined time period from said occurrence of saidsecond event in order to verify that the conditions for said secondevent are fulfilled during the predetermined time period.
 18. The methodaccording to claim 11, comprising configuring the shortened timeintervals after said second event occurs.
 19. The method according toclaim 11, wherein the predetermined time intervals correspond to apredetermined DRX cycle.
 20. A user equipment located in a serving cellof a mobile communications network, comprising: means for monitoringdownlink communication at predetermined time intervals when operating indiscontinuous reception mode, means for performing communicationparameter measurements regarding at least one of the serving cell andone or more neighbor cells, means for sending, after the occurrence of afirst event, at least one of measurement data and a first event reportfrom said user equipment to said network, wherein said sending istriggered by the occurrence of the first event, and means for causingsaid monitoring to be performed at shortened time intervals after theoccurrence of a second event, wherein said second event is defined toindicate a higher probability of receiving a handover command than saidfirst event.
 21. The user equipment according to claim 20, wherein saidfirst event and said second event are defined in relation to saidparameter measurements.
 22. The user equipment according to claim 20,wherein said second event occurs when the difference in measureddownlink signal quality between the serving cell and a neighbor cellreaches a predetermined level.
 23. The user equipment according to claim20, wherein said second event occurs when the measured downlink signalquality deteriorate beyond a predetermined level or when the userequipment transmitted power exceeds a predetermined level.
 24. The userequipment according to claim 20, wherein said second event occurs whenthe user equipment transmitted power exceeds a predetermined level andthe measured downlink signal quality decreases below a predeterminedlevel.
 25. The user equipment according to claim 20, wherein said meansfor monitoring is caused to perform said monitoring at shortened timeintervals after a predetermined time period from said occurrence of saidsecond event.
 26. The user equipment according to claim 25, wherein saidmeans for performing communication parameter measurements is caused tocarry out parameter measurements during said predetermined time period,further comprising means for verifying that the conditions for saidsecond event are fulfilled during the predetermined time period based onsaid parameter measurements.
 27. The user equipment according to claim20, comprising means for allowing said second event to be configured bythe network.
 28. The user equipment according to claim 20, comprisingmeans for allowing the shortened time intervals after said second eventoccurs to be set by the network.
 29. The user equipment according toclaim 20, wherein the predetermined time intervals correspond to apredetermined DRX cycle.
 30. A base station in a serving cell of amobile communications network, whereby a user equipment in the cellmonitors downlink communication at predetermined time intervals whenoperating in discontinuous reception mode and performs communicationparameter measurements regarding at least one of the serving cell andone or more neighbor cells, comprising: means for configuring a firstevent in the user equipment, the occurrence of which triggers sending ofat least one of measurement data and a first event report from the userequipment to the base station, and means for configuring a second eventin the user equipment, the occurrence of which causes said monitoring tobe performed at shortened time intervals, whereby said second event isdefined to indicate a higher probability of sending a handover commandto the user equipment than said first event.
 31. The base stationaccording to claim 30, wherein said first event and said second eventare defined in relation to said parameter measurements.
 32. The basestation according to claim 30, comprising means for configuring saidsecond event to occur when the difference in measured downlink signalquality between the serving cell and a neighbor cell reaches a setlevel.
 33. The base station according to claim 30, comprising means forconfiguring said second event to occur when the measured downlink signalquality deteriorate beyond a predetermined level or when the userequipment transmitted power exceeds a predetermined level.
 34. The basestation according to claim 30, comprising means for configuring saidsecond event to occur when the user equipment transmitted power exceedsa predetermined level and the measured downlink signal quality decreasesbelow a predetermined level.
 35. The base station according to claim 30,comprising means for configuring said monitoring at shortened timeintervals to be caused after a predetermined time period from saidoccurrence of said second event.
 36. The base station according to claim35, comprising means for configuring the parameter measurements to becontinued to be carried out during said predetermined time period fromsaid occurrence of said second event in order to verify that theconditions for said second event are fulfilled during the predeterminedtime period.
 37. The base station according to claim 31, comprisingmeans for configuring the shortened time intervals after said secondevent occurs.
 38. The base station according to claim 31, wherein thepredetermined time intervals correspond to a predetermined DRX cycle.